core: fixes for mentions (initial chat load, update mentions, markdown) (#5603)

* core: fix mentions markdown

* test

* core: fix initial load for the first unread item

* core: fix updating messages with mentions

* fix CPP

* query plans

src/Simplex/Chat/Markdown.hs

@@ -173,7 +173,7 @@ markdownP = mconcat <$> A.many' fragmentP
           '`' -> formattedP '`' Snippet
           '#' -> A.char '#' *> secretP
           '!' -> coloredP <|> wordP
-          '@' -> mentionP
+          '@' -> mentionP <|> wordP
           _
             | isDigit c -> phoneP <|> wordP
             | otherwise -> wordP